The present invention relates to composite filter media and, in particular, to low, medium and high efficiency pleatable composite filter media which include either a low, medium or high efficiency fibrous filtration layer of randomly oriented fibers; and one or more permeable stiffening layers which enable the composite filter media to be pleated and retain its pleats.
Filtration devices such as vehicle passenger compartment air filters, high performance engine air filters, engine oil filters, ASHRAE pleatable filters and the like typically use a pleated high efficiency filtration media for the filtration element. Currently, the pleated high efficiency media normally used in these filtration devices are made from ASHRAE filter media or paper products. These paper products are made by a wet-laid technique wherein fibers, e.g. glass fibers, cellulose and/or polymeric fibers, are dispersed in a water or binder slurry which is stirred to cause the fibers to become thoroughly and randomly mixed with each other. The fibers are then deposited from the water or binder slurry onto a conventional paper making screen or wire as in a Fourdrinier machine or a Rotoformer machine to form a matted paper. The paper formed from the fibers is then dried and wound up into a roll or otherwise collected in a conventional manner for further processing, such as being cut into selected sizes and pleated to form the filtration elements for various types of air, gas and liquid filters. The pleated filter elements made from such papers can exhibit high efficiencies. However, these pleated filter elements have low dirt-holding capacities and exhibit high pressure drops. Accordingly, there has been a need to provide a relatively low cost, high efficiency filter media for these filtration applications which exhibit relatively high dirt-holding capacities and relatively low pressure drops as well as low and medium efficiency filter media which exhibit relatively high dirt-holding capacities and relatively low pressure drops.